Time shift reproduction time controlling method and information reproduction apparatus

ABSTRACT

A time shift reproduction time controlling method and an information reproduction apparatus are disclosed wherein reproduction of data at time which is beyond time shift reproduction possible time is prevented with certainty. An input PCR extraction section extracts a PCR from a reception transport stream and outputs the extracted PCR to a subtractor. An output PCR extraction section extracts a PCR from a transport stream read out from a recording medium and outputs the extracted PCR to the subtractor. The subtractor subtracts time information from the output PCR extraction section from time information from the input PCR extraction section and outputs a result of the subtraction to a comparator. The comparator compares the output of the subtractor and output of a reproduction time control register in which a value indicating a time limit to time shift reproduction is stored with each other and outputs a result of the comparison to a reproduction stopping control section. The reproduction stopping control section performs control for outputting a transport stream outputted from a TS readout section to a video and audio decoder in accordance with the comparison result of the comparator.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This application is a continuation of application Ser. No. 10/436,049,filed May 13, 2003, now pending, and based on Japanese PatentApplication No. 2002-139304, filed May 14, 2002, by Susumu Sakamoto,which is incorporated herein by reference in its entirety. Thisapplication claims only subject matter disclosed in the parentapplication and therefore presents no new matter.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a time shift reproduction timecontrolling method for controlling time shift reproduction time and aninformation reproduction apparatus for controlling time shiftreproduction time for use with a time shift reproduction system whichcan receive and temporarily record image data and sound data onto arecording medium and then reproduce an image and sound withinpredetermined time from the data recorded on the recording medium.

2. Description of the Related Art

Various reception apparatus which receive a digital television (digitalTV) broadcast are available, and some of them have a time shiftreproduction function which can temporarily record received encoded dataonto a recording medium such as a hard disk (HD) and reproduce an imageand sound from the encoded data recorded on the recording medium withintime shift permitting time as a time limit. Use of the time shiftreproduction function eliminates the necessity to effect reception ofencoded data and reproduction of the encoded data simultaneously.Accordingly, even if a user temporarily leaves a reception apparatus ina situation wherein the user uses the reception apparatus to enjoy a TVprogram while the reception apparatus continues reception of encodeddata, when the user subsequently returns to the location of thereception apparatus, the user can enjoy the TV program beginning withthe contents of the TV program recorded at the point of time when theuser left the reception apparatus. In other words, the receptionapparatus can reproduce the program going back to the past by a fixedinterval of time.

However, if the time within which it is permitted to record encoded dataonto a recording medium is not limited, then the encoded data recordedon the recording medium may be re-utilized. For example, there is thepossibility that the encoded data recorded on the recording medium maybe transferred to and re-utilized on another apparatus such as apersonal computer or may be provided from the user to and re-utilized bya third party. Since a provider of a TV program should originallyreceive an equivalent to re-utilization of its TV program, suchre-utilization of encoded data of a user as described above spoils thebenefit of the TV program provider, that is, the benefit based on thecopyright.

Therefore, in order to limit the recording time of encoded data onto arecording medium, a limitation is provided to the storage region of arecording medium in a reception apparatus which has the time shiftreproduction function. For example, such a countermeasure as torepetitively use a storage region for fixed time, that is, to overwritethe storage region with new encoded data for time exceeding the fixedtime.

However, where the countermeasure is taken, encoded data within thestorage region before overwritten with new encoded data can be stolen bysuccessively transferring the encoded data to another storage area or toanother recording medium. Although it becomes more and more significantto protect the copyright of a broadcasting program as popularization ofthe digital broadcasting proceeds, the countermeasure that the storageregion for fixed time is repetitively used does not make a sufficientmethod for copyright protection.

Japanese Patent Laid-Open No. 2000-57059 discloses a system wherein, inorder to prevent copying of encoded data of a broadcasting program orthe like, the program providing side embeds time-of-day information intothe encoded data using an electronic watermark technique and thereception apparatus side reproduces the time-of-day information andprevents reproduction of the encoded data at time of day after more thanfixed time after the time-of-day indicated by the time-of-dayinformation. With the system, however, if the time-of-day information isfalsified, then reproduction of the encoded data is permitted at time ofday after more than the fixed time after the time of day indicated bythe time-of-day information.

Japanese Patent Laid-Open No. 2001-298719 discloses another systemwherein the program providing side transmits transmission time-of-dayinformation together with image data and the reception apparatus sidereproduces the transmission time-of-day information and preventsreproduction of the image data at time of day after more than fixed timeafter the time of day indicated by the transmission time information.Also with the system just described, if the time-of-day information isfalsified, then reproduction of the encoded data is permitted at time ofday after more than the fixed time after the time of day indicated bythe time-of-day information.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a time shift timereproduction time controlling method and an information reproductionapparatus by which reproduction of data at time of day after more thanfixed time exceeding time shift permitting time can be prevented withcertainty.

In order to attain the object described above, according to an aspect ofthe present invention, there is provided a time shift reproduction timecontrol method for controlling a time limit in a case wherein input datais temporarily recorded and the recorded data is read out to performtime shift reproduction of information based on the recorded data,comprising the steps of calculating a difference between time indicatedby time information included in the input data and time indicated bytime information included in the recorded data, and permitting timeshift reproduction if the difference is within a time limit determinedin advance, but inhibiting the time shift reproduction if the differenceis beyond the time limit.

Preferably, the input data is encoded data, and information used forreproduction of a decoding clock signal utilized to decode the encodeddata is used as the time information included in the input data and therecorded data.

Preferably, the input data is reception data of digital broadcasting,and time information included in the digital broadcasting is used as thetime information included in the input data and the recorded data.

The time shift reproduction time control method may be configured suchthat the input data is encrypted and temporarily recorded, and adecryption process is performed for the encrypted recorded data toregenerate the input data upon the time shift reproduction. In thisinstance, even if the encoded data temporarily recorded on the recordingmeans is stolen, reproduction based on the encoded data cannot beperformed.

The time shift reproduction time control method may be configured suchthat time information is produced using the clock signal produced basedon the information used for reproduction of the decoding clock signalutilized to decode the encoded data, and the produced time informationis added to the encoded data to produce the input data to be temporarilyrecorded. In this instance, even if a value of time information becomesnon-continuous upon changeover of a broadcast program or the like,correct time information can be added to the encoded data.

The time shift reproduction time control method may be configured suchthat the input data is formed from a packet data string, and packet datais temporarily recorded except for packet data which is not used forreproduction. In this instance, the capacity of the recording means forrecording the encoded data can be reduced.

The time shift reproduction time control method may be configured suchthat discontinuity of time indicated by the time information included inthe input data is detected, and the discontinuity of time indicated bythe time information is corrected upon the time shift reproduction. Inthis instance, incorrect calculation of time shift reproduction time canbe avoided.

According to another aspect of the present invention, there is providedan information reproduction apparatus includes recording means fortemporarily recording input data, means for implementing a time shiftreproduction function for performing reproduction at a time-of-daydifferent from a recording time-of-day based on the recorded datarecorded by the recording means, and a time information control sectionfor calculating a difference between time indicated by time informationincluded in the input data and time indicated by time informationincluded in the recorded data and permitting time shift reproduction ifthe difference is within a time limit determined in advance butinhibiting the time shift reproduction if the difference is beyond thetime limit.

Preferably, the input data is encoded data, and the time informationcontrol section uses information used for reproduction of a decodingclock signal utilized to decode the encoded data as the time informationincluded in the input data and the recorded data.

Where the input data is reception data of digital broadcasting, theinformation reproduction apparatus may further comprise an input timeinformation extraction section for extracting time information includedin digital broadcasting and outputting the time information to the timeinformation control section and an output time information extractionsection for extracting time information from within the encoded dataread out from the recording means and outputting the time information tothe time information control section.

The information reproduction apparatus may further comprise a timeinformation inserting section for producing time information using aclock signal produced based on information used for reproduction of thedecoding clock signal utilized to decode the encoded data and adding theproduced time information to the encoded data to produce input data tobe temporarily recorded.

Where the input data is formed from a packet data string, theinformation reproduction apparatus may further comprise an informationdeletion section for excepting packet data which is not used forreproduction and an interval regeneration section for regenerating aposition of the packet data on a time axis based on the time informationadded to the encoded data. In this instance, even if discontinuity of avalue of time information occurs upon changeover of a broadcast programor the like, correct time information is added to the encoded data.

The information reproduction apparatus may further comprise correctionmeans for detecting discontinuity of time indicated by the timeinformation included in the input data and correcting the discontinuityof time indicated by the time information upon the time shiftreproduction. In this instance, even if discontinuity of a value of timeinformation occurs upon changeover of a broadcast program or the like,correct time information is added to the encoded data.

The correction means may include input side correction means forcalculating a difference between time indicated by time informationincluded in newly inputted data and time indicated by the timeinformation included in the input data inputted last and storing thedifference if the difference is over a threshold value and time shiftreproduction side correction means for calculating a difference betweentime indicated by time information included in data newly read out fromthe recording means and time indicated by time information included indata read out last from the recording means, and correcting, if thedifference exceeds the threshold value, the time information based onthe difference stored by the input side correction means.

The time information control section may include time limit storagemeans for storing a value which indicates a time limit of the time shiftreproduction, a subtractor for performing a subtraction process betweenthe time information outputted from the input time informationextraction section and the time information outputted from the outputtime information extraction section, and a comparator for comparing avalue stored in the time limit storage means and a result of thesubtraction of the subtractor to decide whether or not the time shiftreproduction should be permitted.

The information reproduction apparatus may further comprise anencryption section for encrypting the input data to be recorded by therecording means, and a decryption section for decrypting the encrypteddata read out from the recording means. In this instance, even if theencoded data temporarily recorded on the recording means is stolen,reproduction based on the encoded data cannot be performed.

The information reproduction apparatus may further comprise a video andaudio decoder for decoding the encoded data to reproduce video data andaudio data and a reproduction stopping control section for stoppingoutputting of the encoded data to the video and audio decoder if thetime shift reproduction is stopped by the time information controlsection.

Preferably, also within a period within which outputting of the encodeddata to the video and audio decoder is stopped, the encoded data is readout from the recording means.

With the time shift reproduction time control method and informationreproduction apparatus of the present invention, the difference betweentime indicated by time information included in input data and timeindicated by time information included in recorded data is calculated,and, if the difference is within a time limit determined in advance,then time shift reproduction is permitted, but, if the difference isbeyond the time limit, then the time shift reproduction is inhibited.Therefore, there is an advantage that reproduction of data at time whichis beyond time shift reproduction possible time can be prevented withcertainty.

Particularly, where information used for reproduction of a decodingclock signal used for decoding encoded data is used as time informationof input data used in order to calculate the difference thereof fromtime indicated by time information included in recorded data, if timeinformation is falsified, then an image and sound cannot be correctlyreproduced. Therefore, the reproduction of data at time which is beyondthe time shift reproduction possible time can be prevented withcertainty.

The above and other objects, features and advantages of the presentinvention will become apparent from the following description and theappended claims, taken in conjunction with the accompanying drawings inwhich like parts or elements are denoted by like reference symbols.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block diagram showing components of a time shiftreproduction system according to the present invention which relate toinputting and outputting of encoded data;

FIG. 2 is a block diagram showing an information reproduction apparatusto which the present invention is applied;

FIG. 3 is a diagrammatic view illustrating a data stream of the MPEG2system;

FIG. 4 is a block diagram showing a detailed configuration of atransport stream reference decoder provided in a video and audio decoderof the information reproduction apparatus of FIG. 2;

FIGS. 5 and 6 are block diagrams showing modifications to theinformation reproduction apparatus of FIG. 2;

FIG. 7 is a signal sequence diagram illustrating a data stream of adigital broadcast;

FIGS. 8 and 9 are block diagrams showing different modifications to theinformation reproduction apparatus of FIG. 2;

FIG. 10 is a diagrammatic view showing a structure of a time offsettable used in the information reproduction apparatus of FIG. 9;

FIG. 11 is a diagrammatic view showing a structure of a time data tableused in the information reproduction apparatus of FIG. 9;

FIG. 12 is a block diagram showing another information reproductionapparatus to which the present invention is applied; and

FIG. 13 is a diagrammatic view illustrating a program stream.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a time shift reproduction system which can carry out a timeshift reproduction time controlling method according to the presentinvention and particularly shows those components which relate toinputting and outputting of encoded data.

Referring to FIG. 1, an encoded data inputting section 1 receivesencoded data of an arbitrary video source designated by a user andoutputs it to an inputted encoded data control section 2. The inputtedencoded data control section 2 extracts time information included in thereceived data, and outputs the time information to a time informationcontrol section 5 and further outputs the received encoded data to anencoded data writing section 3. The encoded data writing section 3writes the inputted encoded data onto a recording medium (recordingmeans) 4 such as a hard disk (HD).

A user will perform an operation for starting reproduction afterarbitrary time shift reproduction time. Information which indicates thefact that the operation just described is performed is inputted to anoutput encoded data control section 7. An encoded data readout section 6reads out the encoded data from the recording medium 4 in response to areadout request of the output encoded data control section 7 based on anoperation of the user and outputs the read out encoded data to theoutput encoded data control section 7. The output encoded data controlsection 7 extracts the time information included in the read out encodeddata and outputs the extracted time information to the time informationcontrol section 5. The time information control section 5 uses the timeinformation received from the inputted encoded data control section 2 astime information at present and uses the time information received fromthe output encoded data control section 7 as time information for timeshift reproduction. Then, the time information control section 5compares the time information at present and the time information fortime shift reproduction with each other to discriminate whether or notthe present time is within a time limit to the time shift reproductiontime, and outputs a result of the discrimination to the output encodeddata control section 7.

If the discrimination result of the time information control section 5is not within the time limit to the time shift reproduction time, thenthe output encoded data control section 7 abandons the encoded data readout from the recording medium 4 or performs controlling for stoppingoutputting of the encoded data to an encoded data outputting section 8.On the other hand, if the discrimination result of the time informationcontrol section 5 is within the time limit to the time shiftreproduction time, then the output encoded data control section 7outputs the encoded data read out from the recording medium 4 to theencoded data outputting section 8. The encoded data outputting section 8passes the encoded data received from the outputted encoded data controlsection 7 to a processing section at the following stage of the timeshift reproduction system, for example, to a decoder.

First Embodiment

FIG. 2 is a block diagram showing an example of a configuration of aninformation reproduction apparatus which can carry out the time shiftreproduction time controlling method according to the present invention.The information reproduction apparatus shown in FIG. 2 is an informationreproduction apparatus which receives a radio wave of a digitalbroadcast and reproduces encoded data from the received radio wave ofthe digital broadcast and then reproduces an image and sound based onthe encoded data. Further, in the information reproduction apparatus ofthe present embodiment, the encoded data is data based on the MPEG2system. However, use of encoded data based on the MPEG2 system is notessentially required in the present invention.

Referring to FIG. 2, a tuner unit 21 ready for a digital broadcast(hereinafter referred to simply as tuner unit 21) reproduces data in theform of a transport stream (hereinafter referred to suitably as TS)including a program selected by a user from within a radio wave of adigital broadcast and outputs the data. An input TS control section 22includes an input PCR (Program Clock Reference) extraction section 30 asan input time information extraction section for extracting timeinformation from the transport stream received from the tuner unit 21. ATS writing section 23 writes the transport stream onto the recordingmedium 4. A TS readout section 26 reads out the transport stream fromthe recording medium 4 in response to a request from an output TScontrol section 27. The output TS control section 27 includes an outputPCR (Program Clock Reference) extraction section 31 as an output timeinformation extraction section for extracting time information includedin the transport stream from the TS readout section 26 and areproduction stopping control section 35 for performing transport streamoutput control to a video and audio decoder 28. A subtractor 32subtracts time indicated by the time information extracted by the outputTS control section 27 from time indicated by the time informationextracted by the input TS control section 22. A reproduction timecontrol register 33 serving as time limit storing means stores areproduction time control value which indicates a time limit. Acomparator 34 compares an output of the subtractor 32 and the storedvalue of the reproduction time control register 27 with each other. Thevideo and audio decoder 28 reproduces the transport stream from theoutput TS control section 27. A television (TV) apparatus 27 serving asa video and audio output section provides a video signal and an audiosignal outputted from the video and audio decoder 28 to a user. It is tobe noted that the subtractor 32, reproduction time control register 33and comparator 34 form the time information control section 5.

The tuner unit 21 particularly receives a radio wave of a digitalbroadcast and performs processes of decoding and error correction toextract encoded data, and outputs the encoded data to the input TScontrol section 22. The extracted data is digital data of such atransport stream of the MPEG2 adopted by digital broadcasting as shownin FIG. 3.

As shown in FIG. 3, the transport stream is formed from a stream oftransport packets having a fixed length of 188 bytes. An adaptationfield is defined at a header part (portion except payload) in eachtransport packet. Time information Program Clock Reference (hereinafterreferred to as PCR) having a length of 42+6 bits is included in theadaptation field.

The input TS control section 22 performs working of a transport streamhaving the structure shown in FIG. 3 and information analysis forallowing a user to receive a desired program from within the transportstream. Further, the input TS control section 22 outputs the transportstream to the TS writing section 23 for storing the data. The PCRextraction section 30 included in the input TS control section 22extracts the time information PCR shown in FIG. 3 from within thetransport stream received from the tuner unit 21 and outputs theextracted time information PCR to the subtractor 32. The TS writingsection 23 outputs the transport stream received from the input TScontrol section 22 to the recording medium 4. The transport stream fromthe TS writing section 23 is recorded onto the recording medium 4.

The TS readout section 26 reads out the transport stream from therecording medium 4 in response to a request from the output TS controlsection 27 and output the read out transport stream to the output TScontrol section 27. The output TS control section 27 issues a readoutrequest for the transport stream to the TS readout section 26 andperforms control for outputting the transport stream to the video andaudio decoder 28. Further, the output TS control section 27 stops theissuance of the readout request to the TS readout section 26 in responseto a temporary stopping operation by a user. Further, if the time of thetime shift reproduction is beyond the time limit, then the output TScontrol section 27 stops the outputting of the transport stream to thevideo and audio decoder 28.

The output PCR extraction section 31 included in the output TS controlsection 27 extracts the time information PCR from within the transportstream received from the TS readout section 26 and outputs the extractedtime information PCR to the subtractor 32. The subtractor 32 subtractsthe time information received from the output PCR extraction section 31from the time information received from the input PCR extraction section30 and outputs a result of the subtraction to the comparator 34. Thereproduction time control register 33 stores time shift permission time,that is, a value which indicates a time limit to the time shiftreproduction for every received program. The comparator 34 compares anoutput of the subtractor 32 and an output of the reproduction timecontrol register 33 with each other and outputs a result of thecomparison to the reproduction stopping control section 35. Thereproduction stopping control section 35 performs control for outputtingthe transport stream outputted from the TS readout section 26 to thevideo and audio decoder 28 in accordance with the comparison result ofthe comparator 34. The video and audio decoder 28 decodes encoded dataof an image and sound included in the transport stream outputted fromthe output TS control section 27 and outputs the decoded data to a TVapparatus 29. The TV apparatus 29 provides the image and sound to theuser.

FIG. 4 is a block diagram showing a configuration of, for example, a TSreference decoder 28 a included in the video and audio decoder 28. TheTS reference decoder 28 a receives time information PCR included in atransport stream and places the time information PCR into a counter(STC: System Time Clock) 271. A phase comparator 272 compares theinputted time information PCR and the set value of the counter 271 witheach other and outputs a phase difference which is a result of thecomparison to a digital to analog (D/A) converter 273. The D/A converter273 outputs an analog signal which indicates the phase difference to aVCO (Voltage Controlled Oscillator) 275 through an LPF (low-pass filter)274. The VCO 275 acts to eliminate the phase difference and outputs aresulting clock signal. By such a PLL (phase-locked loop) configurationas just described, the TS reference decoder 28 a can reproduce a systemclock signal (decoding clock signal) having a frequency of 27 MHz basedon the time information PCR.

Subsequently, action of the information reproduction apparatus of thepresent embodiment is described with reference to FIGS. 2 and 3. If auser selects a program which the user wants to enjoy, then the tunerunit 21 receives a radio wave in which the selected program is includedand performs demodulation and error correction for the received radiowave and then outputs a resulting transport stream to the input TScontrol section 22. The input TS control section 22 analyzes informationnecessary for receiving the program and outputs only the transportstream necessary for storage to the TS writing section 23. The input PCRextraction section 30 included in the input TS control section 22extracts the time information PCR shown in FIG. 3 from within thetransport stream necessary for receiving the program. Here, low-order 33bits in the time information PCR are extracted and outputted to thesubtractor 32. Information indicated by the time information PCR to beoutputted to the subtractor 32 is information which indicates presenttime-of-day at which the broadcast is being received at present. In theinformation reproduction apparatus of the present embodiment, thepresent time information based on the time information PCR beingreceived at present and the time information based on the timeinformation PCR for the time shift reproduction are compared with eachother to calculate time shift elapsed time.

The transport stream outputted from the input TS control section 22 isrecorded onto the recording medium 4 by the TS writing section 23. TheTS readout section 26 reads out the transport stream from the recordingmedium 4 in accordance with a request from the output TS control section27 and outputs the read out transport stream to the output TS controlsection 27. The output TS control section 27 issues, after the timeshift reproduction time based on the operation of the user elapses, a TSreadout request to the TS readout section 26 and receives the transportstream to be reproduced. The output PCR extraction section 31 extractsthe time information PCR from the transport stream to be reproduced andsends the extracted time information PCR to the subtractor 32. Theinformation indicated by the time information PCR to be sent to thesubtractor 32 is information which indicates time later in the timeshift reproduction with respect to the information indicated by the timeinformation PCR outputted from the input PCR extraction section 30. Thesubtractor 32 subtracts the time information PCR transmitted theretofrom the output PCR extraction section 31 from the time information PCRtransmitted thereto from the input PCR extraction section 30 andtransmits a result of the subtraction to the comparator 34. Thesubtraction result outputted to the comparator 34, that is, timedifference information, corresponds to the reproduction shift time inthe time shift reproduction based on the operation of the user.

Thirty-three bits of the PCR represent a value of a 33-bit counter whichincrements by one with 300 clocks of a 27-MHz clock signal which is usedwhen a broadcasting station encodes and compresses a program.Accordingly, counting of 2³³/(27×10⁶/300) seconds (=approximately 26hours) can be performed. In other words, counting for 24 hours can besufficiently performed.

As shown in FIG. 4, in a reception system, the time information PCR isused in order to produce a decoding clock signal which is synchronizedin phase with a frequency of a clock signal used for encoding. Further,in the information reproduction apparatus of the present embodiment,time shift reproduction time control is performed using the timeinformation PCR. Accordingly, if, in order to cancel a time shiftreproduction time limit, contents of the time information PCR arechanged at a preceding stage to the output TS control section 27 or thelike, then production of an encoding clock signal is not performednormally. As a result, in the video and audio decoder 28 and so forthprovided at a following stage, an internal buffer or the like suffersfrom underflow, overflow or the like to cause a disorder in reproductionof an image and sound. In particular, if an operation for deceiving thetime shift reproduction time limit is performed, then a problem thatreproduction of an image and sound is disordered occurs. In other words,falsification of time information for misrepresenting the time shiftreproduction time limit can be prevented.

When a limit is to be added to time shift reproduction time, a valuecorresponding to a time limit to the time shift reproduction time isplaced into the reproduction time control register 33. For example, iftime shift reproduction beyond 90 minutes is to be inhibited, then avalue corresponding to 90 minutes is placed into the reproduction timecontrol register 33. In the information reproduction apparatus of thepresent embodiment, since 300 clocks of the 27-MHz clock signalcorresponds to 1, 90×60×(27×10⁶/300)=1CF7C580 (hexadecimal number) isstored. For example, if information for adding a limit to the time shiftreproduction time is transmitted from a contents provider such as abroadcasting station, then a time limit may be placed into thereproduction time control register 33.

It is to be noted that all of the 33 bits need not necessarily be usedfor the comparison, but, for example, only 16 higher order bits may beused for the comparison. If the 16 higher order bits are used, then theaccuracy of the time shift reproduction time is approximately 1.6seconds. However, the scale of the circuit can be reduced.

The comparator 34 outputs a result of comparison between an output fromthe subtractor 32 and a set value of the reproduction time controlregister 33 to the reproduction stopping control section 35. Thereproduction stopping control section 35 performs controlling foroutputting or stopping the transport stream to the video and audiodecoder 28 in accordance with the comparison result of the comparator34. In particular, if the time of the time shift reproduction is withinthe time limit, then the transport stream is outputted, and as a result,the user can perform the time shift reproduction. However, if the timeshift reproduction time is beyond the time limit, then outputting of thetransport stream is stopped. Consequently, the user cannot perform thetime shift reproduction. It is to be noted that the comparison result ofthe comparator 34 corresponds to a result of discrimination of whetheror not the time shift reproduction should be allowed.

Also during outputting stopping control of the transport stream, theoutput TS control section 27 continues issuance of a readout request tothe TS readout section 26. As a result, a portion of the transportstream which is beyond the time limit to the time shift reproduction isignored, but time shift reproduction only of a portion of the transportstream within the time limit is automatically performed.

First Modification to the First Embodiment

Now, a modification to the information reproduction apparatus of thefirst embodiment is described with reference to a block diagram of FIG.5. In the information reproduction apparatus of the embodiment shown inFIG. 2, if a time limit to the time shift reproduction is exceeded, thenan image and sound cannot be reproduced. However, if data stored in therecording medium 4 is extracted from the information reproductionapparatus before it is reproduced, then there is the possibility thatthe data may be reproduced by another reproduction system. Therefore,the modified information reproduction apparatus is configured such that,as shown in FIG. 5, an encryption section 61 for performing encryptionof data is provided intermediately on the path from the TS writingsection 23 to the recording medium 4, and a decryption section 62 fordecrypting the encrypted data is provided intermediately on the pathfrom the recording medium 4 to the TS readout section 26. The othercomponents in the information reproduction apparatus are similar tothose shown in FIG. 2.

In the present modified information reproduction apparatus, just beforea transport stream is temporarily recorded onto the recording medium 4for the time shift reproduction, encryption is performed for thetransport stream to be recorded. Further, just before the time shiftreproduction is performed, the transport stream read out from therecording medium 4 is decrypted. Accordingly, the informationreproduction apparatus in the present modification is configured suchthat, even if the transport stream temporarily recorded on the recordingmedium 4 is stolen, reproduction based on the transport stream cannot beperformed. It is to be noted that the present modified informationreproduction apparatus acts in a similar manner to that of theinformation reproduction apparatus of the first embodiment except thatjust described.

Second Modification to the First Embodiment

The information reproduction apparatus of the first embodiment describedabove may be modified also in such a manner as seen in FIG. 6. While, inthe information reproduction apparatus of the first embodiment and thefirst modification, time information PCR included in a transport streamis used to control the time shift reproduction time, in the presentmodified information reproduction apparatus, time information whichindicates a distance (position on the time base) of a transport packetis added to the top of each transport packet as seen in FIG. 7.

In the following, only differences of the present modified informationreproduction apparatus from the information reproduction apparatus ofthe embodiment described above are described. Referring to FIG. 6, thepresent modified information reproduction apparatus is different fromthe information production apparatus of the first embodiment of FIG. 2in that it includes an input TS control section 42, an output TS controlsection 47 and a time information control section 51 in placed of theinput TS control section 22, output TS control section 27 and timeinformation control section 5, respectively. The time informationcontrol section 51 additionally includes a system counter 72 of 27 MHz.Meanwhile, the input TS control section 42 includes, in place of theinput PCR extraction section 30, a time information addition section 71for producing time information using a count value from the systemcounter 72 and adding the produced time information to the top of eachtransport packet as shown in FIG. 7. Further, the output TS controlsection 47 includes, in place of the output PCR extraction section 31, atime information extraction section 73 for extracting the timeinformation added to the top of each transport packet and sending theextracted time information to the subtractor 32.

The system counter 72 produces a count value based on time informationPCR using a decoding clock signal (27 MHz) synchronized with an encodingclock signal for image data and sound data used in a broadcastingstation. Further, the system counter 72 is formed, for example, from 40bits, and performs count-up using the decoding clock signal.

The time information produced by the time information addition section71 is utilized also for regenerating the distance of each transportpacket. As shown in FIG. 7, transport streams used for broadcastinginclude also a transport stream which does not relate to a receptionprogram selected by the user (refer to the first stage of FIG. 7). It isnot necessary to record the transport stream, which does not relate tothe reception program selected by the user, onto the recording medium 4.Accordingly, if, when a transport stream is to be recorded onto therecording medium 4, the transport stream not relating to the receptionprogram selected by the user is erased, then the capacity necessary forrecording can be reduced.

However, if the transport stream not relating to the reception programselected by the user is recorded onto the recording medium 4, thencontinuity of time information based on the time information PCR intransport streams recorded on the recording medium 4 is spoiled. Inparticular, a transport stream which is in a state wherein informationwhich indicates an interval of a transport stream upon broadcasting isnot normal is recorded onto the recording medium 4. Accordingly, in thiscase, if the transport stream is read out from the recording medium 4,then transport packets thereof cannot be regenerated with a correct timeinterval.

Therefore, in the present modified information reproduction apparatus,the time information addition section 71 adds time information whichindicates an interval of each transport packet to the top of thetransport packet. It is to be noted that, though not shown in FIG. 7,the time information addition section 71 adds the time information toall of transport packets. Meanwhile, as shown in the third stage of FIG.7, the input TS control section 42 outputs only a transport stream whichrelates to the reception program selected by the user to the TS writingsection 23. Accordingly, the input TS control section 42 also implementsa function as an information reduction section for removing packet datanot used for reproduction. It is to be noted that, in the presentmodified information reproduction apparatus, data outputted from theinput TS control section 42 corresponds to input data including timeinformation.

Only a transport stream relating to the reception program selected bythe user is recorded onto the recording medium 4. The output TS controlsection 47 regenerates an interval of each transport packet (refer tothe second stage of FIG. 7) based on the time information added to thetransport stream read out from the recording medium 4. For example, theoutput TS control section 47 outputs a next transport packet to thevideo and audio decoder 28 later, with respect to a time point at whicha certain transport packet is outputted to the video and audio decoder28, by time of a difference between the time information added to thetransport packet and the time information added to the next transportpacket. Accordingly, the output TS control section 47 also has afunction as an interval regeneration section for regenerating aninterval of packet data (position on the time base) based on timeinformation added to encoded data.

If the time information added to the top of a transport packet is usedonly for regeneration of an interval of the transport packet, then,where a system clock of 27 MHz is used, approximately 32 bits aresufficient for the time information. If 32 bits are used, then countingof 232/(27×10⁶) seconds (approximately 159 seconds) can be performed.However, if the time information is expanded to 40 bits, then the timeinformation can be used for control of time shift reproduction time. If40 bits are used, then counting of 24°/(27×10⁶) seconds (approximately11 hours) can be performed.

The time information added to the top of each transport packet is usedfor regenerating the interval of the transport packet to be reproduced.Therefore, if the time information is falsified, then, underflow oroverflow of an internal buffer occurs in the video and audio decoder 28,and an error that an image and sound are not reproduced normally occurs.Consequently, also in the present modified information reproductionapparatus, falsification of the time information can be preventedsimilarly as in the information reproduction apparatus of the firstembodiment and the first modification.

The system counter 72 always performs count-up based on a decoding clocksignal produced in the information reproduction apparatus. Accordingly,even if the value of the time information PCR becomes discontinuous uponchangeover of a broadcast program or the like, correct time informationcan be added to the top of the transport packet.

Third Modification to the First Embodiment

The information reproduction apparatus of the first embodiment describedabove may be modified also in such a manner as seen in FIG. 8. Theinformation reproduction apparatus of the present modification isdifferent from the information reproduction apparatus of the firstembodiment only in that it includes, in place of the time informationcontrol section 5, a time information control section 52 for comparingtime information PCR upon reception, that is, time information PCRoutputted from the input TS control section 22, and time information PCRupon time shift reproduction, that is, time information PCR outputtedfrom the output TS control section 27, with each other.

If the place of electric wave signaling equipment is changed over uponchangeover of a program or because of a local downpour of rain or in alike case, then there is the possibility that discontinuity of timeindicated by the time information PCR may occur. In the informationreproduction apparatus of the embodiment and the first modification, ifdiscontinuity of time indicated by time information PCR occurs, thentime shift reproduction time is calculated but incorrectly. However,with the present modified information reproduction apparatus, suchincorrect calculation as just described can be avoided.

In the following, description is given only of the difference of thepresent modified information reproduction apparatus from the informationreproduction apparatus of the embodiment described above. Referring toFIG. 8, the time information control section 52 includes, in addition toa subtractor 32, a reproduction time control register 33 and acomparator 34 described hereinabove with reference to FIG. 2, a newinput PCR register 91 for storing time information PCR outputted fromthe input TS control section 22 and transferring different timeinformation PCR set in advance therein, an old input PCR register 92 forstoring a value of input time information PCR received last from the newinput PCR register 91, a subtractor 93 for calculating the differencebetween the value stored in the new input PCR register 91 and the valuestored in the old input PCR register 92, a PCR difference thresholdvalue register 94 for storing a threshold value to be used fordiscrimination that the PCR difference value calculated by thesubtractor 93 is a discontinuous value, a comparator 95 for comparing anoutput of the subtractor 93 and the stored value of the threshold valueregister 94 with each other, a discontinuity detection interruptgeneration section 96 for issuing a notification that discontinuity ofthe time information PCR occurs to software based on a result of anoutput of the comparator 95 and outputting a storing instruction of thePCR difference value when the discontinuity occurs, and a discontinuitydifference value register 98 for storing an output (PCR differencevalue) of the subtractor 93 in response to an instruction from thediscontinuity detection interrupt generation section 96. The componentsdescribed above correspond to correction means on the reception side(input side correction means) which detects discontinuity of timeindicated by time information included in input data. Further, thecomponents from the tuner unit 21 to the recording medium 4 correspondto those on the reception side.

Further, the time information control section 52 includes a new outputPCR register 99 for storing time information PCR outputted from theoutput TS control section 27 and transferring different time informationPCR stored in advance, an old output PCR register 100 for storing avalue of the time information PCR transferred from the new output PCRregister in the last cycle, a subtractor 101 for calculating adifference between the value stored in the new output PCR register 99and the value stored in the old output PCR register 100, a comparator102 for comparing an output of the subtractor 101 and the stored valueof the PCR difference threshold value register 94 with each other, acorrection value register 103 in which a difference correction value tobe used upon occurrence of discontinuity of the time information PCR isset in advance and which corrects the time information PCR when it isdiscriminated from a result of the comparator 102 that discontinuity ofthe time information PCR occurs, a discontinuity correction controlsection 104 for outputting the value of the correction value register103 based on a result of the comparison of the comparator 102, and anadder 105 for adding the correction value outputted from thediscontinuity correction control section 104 to the time information PCRfor time shift reproduction. The components described above correspondto correction means on the time shift reproduction side for correctingdiscontinuity of time indicated by time information. Further, thecomponents from the recording medium 4 to the video and audio decoder 28correspond to those on the time shift reproduction side.

It is to be noted that the value of the discontinuity difference valueregister 98 at a point of time when a notification issued from thediscontinuity detection interrupt generation section 96 is received isset by software to the correction value register 103. The software justmentioned is a control section including a CPU not shown in FIG. 8. Itis to be noted that the value of the discontinuity difference valueregister 98 may be transferred otherwise by hardware to the correctionvalue register 103.

Next, action of the present modified information reproduction apparatusis described. A sufficiently higher value than a fluctuation value ofthe time information PCR when a normal program is received is set inadvance to the PCR threshold value register 94 by software. In the timeinformation control section 52, if discontinuity of the time informationPCR occurs on the reception side, then the first time information PCRwhen the discontinuity occurs is stored as new time information PCR intothe new input PCR register 91. It is assumed that, at this time, suchhigh old time information PCR that the difference thereof from new inputtime information PCR exceeds the stored value of the PCR differencethreshold value register 94 is stored in the old input PCR register 92.

Accordingly, a result of subtraction outputted from the subtractor 93 isa value which exceeds the stored value of the PCR difference thresholdvalue register 94. The comparator 95 compares the stored value of thePCR difference threshold value register 94 and the subtraction result ofthe subtractor 93 with each other and outputs a result of the comparisonto the discontinuity detection interrupt generation section 96. Thediscontinuity detection interrupt generation section 96 issues, if itdiscriminates based on the comparison result of the comparator 95 thatdiscontinuity of time indicated by the time information PCR occurs, aninstruction to store an output value of the subtractor 93 into thediscontinuity difference value register 98 and issues an interruptionnotification for notifying the software of the fact that discontinuityof time indicated by the time information PCR occurs. The software readsout the stored value of the discontinuity difference value register 98in response to the notification from the discontinuity detectioninterrupt generation section 96 and sets the read out value to thecorrection value register 103.

In this case, discontinuity of time indicated by the time informationPCR occurs on the time shift reproduction side after time shiftreproduction time. If discontinuity of time indicated by the timeinformation PCR occurs, then the first time information PCR after thediscontinuity occurs is stored into the new output PCR register 99first. At this time, such old time information PCR that the differencethereof from the new input PCR exceeds the stored value of the PCRdifference threshold value register 94 is stored in the old output PCRregister 100. The subtractor 101 outputs a result of the subtractionbetween the stored value of the new output PCR register 100 and thestored value of the old output PCR register 100.

The comparator 102 compares the stored value of the PCR differencethreshold value register 94 and the subtraction result of the subtractor101 with each other and outputs a result of the comparison to thediscontinuity correction control section 104. The discontinuitycorrection control section 104 outputs, if it discriminates based on theoutput value of the subtractor 101 that discontinuity of time indicatedby the time information PCR occurs, the value stored in the correctionvalue register 103 to the adder 105. The adder 105 adds the correctionvalue to the stored value of the new output PCR register 99 and outputsa result of the addition as time information PCR for the time shiftreproduction to the subtractor 32. The difference value at a point oftime when discontinuity of time indicated by the time information PCRoccurs upon reception of a broadcast is stored in the correction valueregister 103. Consequently, by such control as described above,discontinuity of the time information PCR on the time shift reproductionside is eliminated.

Accordingly, in the present modified information reproduction apparatus,even if discontinuity of a value of the time information PCR occurs uponchangeover of a broadcast program or the like, time shift reproductiontime can be calculated normally.

Fourth Modification to the First Embodiment

The information reproduction apparatus of the first embodiment describedabove may be modified also in such a manner as seen in FIG. 9. Theinformation reproduction apparatus of the present modification isdifferent from the information reproduction apparatus of the firstembodiment in that it includes, in place of the input TS control section42 and the output TS control section 47, an input TS control section 142including an input TOT/input TDT extraction section 111 and an output TScontrol section 147 including a reproduction stopping control section 35and an output TOT/output TDT extraction section 112, and hence in that,while the time information used in the information reproductionapparatus described above is time information PCR applied in the MPEG2,Time Offset Table (hereinafter referred as TOT) information and TimeDate Table (hereinafter referred to as TDT) information are used. TheTOT and TDT are defined by the ARIB STD-B10 which prescribes programarrangement information prescribed for BS/CS digital broadcasting.

The TOT has a structure shown in FIG. 10 and includes presenttime-of-day information of 24 bits. Meanwhile, the TDT has a structureshown in FIG. 11 and includes, similarly to the TOD, present time-of-dayinformation of 24 bits. Accordingly, if the TOT and TDT are used, thenadvantages similar to those of the information reproduction apparatusdescribed hereinabove can be obtained. However, the time information inthe information reproduction apparatus of the present embodiment (thatis, TOT/TDT) is not used for reproduction of a decoding clock signal andso forth. Therefore, falsification of time information can be easilyperformed in comparison with that of the information reproductionapparatus described hereinabove. Further, while the transmissioninterval of time information PCR is 100 ms, the transmission interval ofthe TOT and TDT is an interval in a unit of second. Therefore, the timecontrol accuracy is reduced. However, since the bit number of the timeinformation is as small as 24 bits, there is an advantage that thecircuit scale can be reduced. Further, also the time information handledis in a unit of second, and also date information is included in the TOTand TDT (refer to FIGS. 10 and 11). Therefore, there is an advantagethat long time management can be performed in time shift time control incomparison with those in the information reproduction apparatusdescribed above.

It is to be noted that the manner of control regarding the time shiftreproduction is similar to that of the information reproductionapparatus of the embodiment and the first modification describedhereinabove.

Second Embodiment

Referring now to FIG. 12, there is shown another informationreproduction apparatus to which the present invention is applied. Theinformation processing apparatus according to the present embodiment is,different from the information processing apparatus of the firstembodiment and the modifications to it, applied to an analog broadcast.The information reproduction apparatus shown includes an analogbroadcast ready tuner unit (hereinafter referred to simply as tunerunit) 131 for receiving an analog broadcast and outputting an imagesignal and a sound signal, a video and audio encoder 132 for encodingthe image signal and sound signal, for example, in accordance with theMPEG2 method and outputting a program stream (hereinafter referred tosuitably as PS) having a structure shown in FIG. 13, an input PS controlsection 133 including an input SCR extraction section 137, whichextracts time information System Clock Reference (hereinafter referredto as time information SCR) from within a program stream, for analyzinga program stream outputted from the video and audio encoder 132, a PSwriting section 134 for recording the program stream onto the recordingmedium 4, a PS readout section 135 for reading out the program streamfrom the recording medium 4, an output PS control section 136 includingan output SCR extraction section 138 for extracting time information SCRfrom the program stream read out from the recording medium 4 and areproduction stopping control section 35, a time information controlsection 5 including a subtractor 32, a reproduction time controlregister 33 and a comparator 34, a video and audio encoder 28, and a TVapparatus 29.

Now, action of the information reproduction apparatus of the presentembodiment is described. If a user selects a program, then the tunerunit 131 outputs an image signal and a sound signal of the selectedprogram. The video and audio encoder 132 encodes the image signal andthe sound signal. While any one of a program stream and a transportstream can be used as an output of the video and audio encoder 132, inthe present information reproduction apparatus, a program stream isused. A program stream has a structure wherein each pack is formed froma pack header, an image packet and a sound packet as seen in FIG. 13.Further, the video and audio encoder 132 produces time informationusing, for example, a clock function built-in the informationreproduction apparatus and uses the produced time information as thetime information SCR. It is to be noted that, in the present informationreproduction apparatus, encoded data outputted from the video and audioencoder 132 corresponds to input data including time information.

The input PS control section 133 performs information analysis of theprogram stream outputted from the video and audio encoder 132 in asimilar manner as in the information analysis performed for a transportstream by the input TS control sections 22 and 42 in the informationprocessing apparatus described hereinabove. The input SCR extractionsection 137 extracts time information SCR shown in FIG. 13 from withinthe program stream and outputs the time information SCR to thesubtractor 32. Further, the input SCR extraction section 137 outputs theprogram stream to the PS writing section 134. The PS writing section 134writes the received program stream onto the recording medium 4. The PSreadout section 135 reads out, in response to a readout request from theoutput PS control section 136, the program stream from the recordingmedium 4 and outputs it to the output PS control section 136. The outputPS control section 136 performs information analysis of the receivedprogram stream in a similar manner as in the information analysisperformed for a transport stream by the output TS control sections 27and 47 in the information processing apparatus described hereinabove.The output SCR extraction section 138 extracts time information SCR fromwithin the program stream and outputs it to the subtractor 32. It is tobe noted that the action of the time information control section 5formed from the subtractor 32, reproduction time control register 33 andcomparator 34 is similar to that of the information processing apparatusof the first embodiment and the first modification to the firstembodiment.

Accordingly, similarly to the reproduction stopping control section 35in the information processing apparatus of the first embodiment and thefirst modification to the first embodiment, the reproduction stoppingcontrol section 35 in the output PS control section 136 performs programstream output control to the video and audio decoder 28 in accordancewith a result of the outputting of the comparator 34. In particular, ifthe time of the time shift reproduction is within the time limit, thenthe program stream is outputted, and as a result, the user can performthe time shift reproduction. However, if the time shift reproductiontime is beyond the time limit, then the outputting of the program streamis stopped. Consequently, the user cannot perform the time shiftreproduction any more. Also during the outputting stopping control of aprogram stream, the output PS control section 137 continues issuance ofthe readout request for a program stream to the PS readout section 136.As a result, a portion of the program stream which is beyond the timelimit to the time shift reproduction is ignored, but time shiftreproduction only of a portion of the program stream within the timelimit is automatically performed.

As described above, according to the information reproduction apparatusof the present embodiment, the time control of the time shiftreproduction can be performed also for an analog broadcast.

As described above, in the information reproduction apparatus of theembodiments and the modifications described above, a time limit to thetime shift reproduction is observed with certainty. Since the timeinformation management and output control of encoded data to the videoand audio decoder 28 are performed by hardware, reproduction of atemporarily recorded stream which is beyond a time limit to the timeshift reproduction can be reliably prevented.

Further, if time information is falsified, then an image and soundcannot be correctly reproduced. In particular, since time informationfor producing a decoding clock signal synchronized with an encodingclock used for encoding of an image signal and a sound signal by abroadcast station is used for management of time shift time, if timeinformation of a temporarily recorded stream is falsified, then an errorin reproduction occurs.

Furthermore, an information reproduction apparatus wherein a time limitto time shift reproduction is observed with certainty can be implementedsimply. This is because the information reproduction apparatus can beimplemented by adding a time information remaining function, asubtractor, a comparator, and an output control function of encodeddata.

It is to be noted that the information reproduction apparatus accordingto the second to fourth modifications to the first embodiment and thesecond embodiment may be modified such that, similarly as in theinformation reproduction apparatus of the first modification to thefirst embodiment, input data is encrypted and recorded onto therecording medium 4 and the encrypted data read out from the recordingmedium 4 is decrypted to regenerate the input data.

While preferred embodiments of the present invention have been describedusing specific terms, such description is for illustrative purposesonly, and it is to be understood that changes and variations may be madewithout departing from the spirit or scope of the following claims.

1. A time shift reproduction time controlling method for digitalbroadcasting for controlling a time limit in a case wherein receptiondata of digital broadcasting which includes time information istemporarily stored into recording means and the data recorded in therecording means is read out to perform time shift reproduction ofinformation based on the recorded data, comprising the steps of:extracting, when time shift reproduction of information based on therecorded data recorded in the recording means is to be performed, thetime information included in the recorded data; calculating a differencebetween time indicated by the extracted time information and timeindicated by the time information included in the reception datacurrently received; and permitting the time shift reproduction of theinformation if the calculated difference is within the time limitdetermined in advance; but inhibiting the time shift reproduction if thedifference exceeds the time limit.
 2. A time shift reproduction timecontrolling method as claimed in claim 1, wherein time information thatis not included in the digital broadcasting is used as the timeinformation included in the recorded data.
 3. A time shift reproductiontime controlling method as claimed in claim 2, wherein time informationthat is used as the time information included in the recorded data isobtained from built-in clock function at the time of encoding the datarecorded in the recording means.
 4. A time shift reproduction timecontrolling method as claimed in claim 1, wherein the data recorded inthe recording means has been encrypted, and a decryption process isperformed for the encrypted recorded data to regenerate the recordeddata upon the time shift reproduction.
 5. A time shift reproduction timecontrolling method as claimed in claim 1, wherein time information isproduced using a clock signal produced based on the information used forreproduction of the decoding clock signal utilized to decode the encodeddata, and the produced time information is added to the encoded data toproduce the input data to be temporarily recorded.
 6. A time shiftreproduction time controlling method as claimed in claim 1, wherein adecoding clock signal is produced from the recorded data that issynchronized in phase with the frequency of the clock signal used forthe reception data.
 7. A reproduction apparatus for digital broadcastingrecording information which includes recording means for temporarilyrecording reception data of digital broadcasting which includes timeinformation and has a time shift reproduction function for performingreproduction at time displaced from the recording time based on therecorded data recorded in said recording means, comprising: timeinformation extraction means for extracting, when time shiftreproduction of information based on the recorded data recorded in therecording means is to be performed, the time information included in therecorded data; and time information control means for calculating adifference between time indicated by the extracted time information andtime indicated by the time information included in the reception datacurrently received and permitting the time shift reproduction of theinformation if the calculated difference is within the time limitdetermined in advance but inhibiting the time shift reproduction if thedifference exceeds the time limit.
 8. A reproduction apparatus asclaimed in claim 7, wherein time information that is not included in thedigital broadcasting is used as the time information included in therecorded data.
 9. A reproduction apparatus as claimed in claim 8,wherein time information that is used as the time information includedin the recorded data is obtained from built-in clock function at thetime of encoding the data recorded in the recording means.
 10. Areproduction apparatus as claimed in claim 7, wherein the data recordedin the recording means has been encrypted, and a decryption process isperformed for the encrypted recorded data to regenerate the recordeddata upon the time shift reproduction.
 11. A reproduction apparatus asclaimed in claim 7, wherein time information is produced using a clocksignal produced based on the information used for reproduction of thedecoding clock signal utilized to decode the encoded data, and theproduced time information is added to the encoded data to produce theinput data to be temporarily recorded.
 12. A time shift reproductiontime controlling method as claimed in claim 1, wherein a decoding clocksignal is produced from the recorded data that is synchronized in phasewith the frequency of the clock signal used for the reception data.